Circuit for use in automatic signalling systems



April 2, 1957 R'. B. BUCHNER CIRCUIT FOR USE IN AUTOMATIC SIGNALLIN GSYSTEQMS Filed July 22, 1952 3 Sheets-Sheet l m VEN roe Aaaze'r BER razaflue/ use April 2, 1957 C R. B. BUCHNER CIRCUIT FOR USE IN AUTOMATICSIGNALLING SYSTEMS Filed July 22, 1952 3 Sheets-Sheet 2rllllllllliIllllllll lllll I II II foam: fizerozo flue/mm MI QIF/V April2, 1957 I I R. B. BUCHNER 2,787,661

CIRCUIT FOR USE IN AUTOMATIC SIGNALLING SYSTEMS Filed July 22, 1952 3Sheets-Sheet 3 Reefer Bur-am Bl/C/l/VEB CIRCUIT FOR USE IN AUTOMATICSIGNALLHIG YSTEMS Robert Bertold lluchner, Hilversum, Netherlands, as-

signor, by mesne assignments, to North American Philips Company, inc,New York, N. Y., a corporatiou oi Delaware Application July 22, 1952,Serial No. 300,173

Claims priority, application Netherlands August 4, 1951 4 Claims. (Cl.179 18) This invention relates to circuits for use in automaticsignalling systems and comprising at least two stages of group selectorsin cascade, of which the numerical adjustment is control-led by aregister.

In, automatic telephone circuits of known types used in exchangescomprising more than 1,000 connections, numerical connection between aconnecting circuit and a subscribers line is established by way of atleast two stages of group selectors and one stage of final selectors,the outlets of the group selectors being connected to selectors of thesubsequent stage. In setting-up numerical connections, the selectors aresuccessively adjusted in cascade, the group selectors selecting a freeoutlet in conformity with a single digit of the number of the desiredsubscriber from the group giving access to the desired direction oftrafic, the final selectors being adjusted in accordance with twodigits. The number of selectors per selecting stage is dete mined by themaximum chance of stagnation which is permissible and which may be, forexample, 0.002, i. e., the possibility that the equipment, due to busyconditions, is unable to complete a call is two out of a thousand calls.

The object of the present invention is to provide a circuit for use insuch systems to obtain a material saving in selectors by the use ofdirect connections between outlets of selectors of several selectingstages. It is thus possible to route a comparatively large proportion ofthe connections outside determined selecting stages, so that the latterhave to deal with only a comparatively lowdensity traflic.

Circuits are known for the connection of telephone exchanges in whichuse is made of overflow connections, in which case two exchanges aredirectly interconnected by lines through which trafiic between theexchanges preferably takes place. If, however, all the direct lines arebusy, additional traffic is routed through a third exchange. This steppermits of economy of the direct lines, but does not provide any savingin selecting equipment.

Circuits are also known which utilise secondary line switches in orderto increase the number of lines accessible by way of outlets of groupselectors. In this case, a plurality of lines are connected directly tooutlets of group selectors, other outlets thereof having connected tothem inlets of secondary line switches which via their outlets giveaccess to further lines. The outlets of the secondary line switches arenot divided into numerical groups. This circuit also does not provideany saving in selectors.

According to the invention, a circuit for use in automatic signallingsystems comprising at least two stages of group selectors in cascade, ofwhich the numerical adjustment is controlled by a register, theselectors of the last group selecting stage and the outlets of theselectors concerned being divided into a plurality of numerical groupsand the inlets of the selectors of the last group selecting stage beingaccessible by way of outlets of United States Patent G Patented Apr. 2,1957 2 selectors of the first group selecting stage in the cascade, ischaracterised in that the outlets of selectors of the last groupselecting stage are connected directly to outlets of selectors of thefirst group selecting stage. These connections are made in such mannerthat each group selector of the first group selecting stage has directaccess to at least one outlet of each numerical group of outlets or" allselectors of the last group selecting stage. The register establishes anumerical connection between the inlet of a selector of the first groupselecting stage and a numerically desired outlet of the last groupselecting stage, and if no such outlet is free, adjusts the selector ofthe first group selecting stage to a free outlet giving access to thedesired numerical direction to which the inlet of a selector of thenext-following group selecting stage in the cascade is connected.

The invent-ion will now be described with reference to the accompanyingdiagrammatic drawings, in which:

Fig. 1 illustrates a known method of establishing a connection betweentwo subscribers,

Fig. 2 shows a circuit according to the invention for use in an exchangecomprising more than 1,000 connections,

Fig. 3 is a circuit for controlling selectors such as may be used in thecircuit shown in Fig. 2,

Fig. 4 showsv a circuit according to the invention for a systemcomprising a plurality of local exchanges, and

Fig. 5 is a circuit for a telephone exchange comprising 9,000connections, in which a circuit according to the invention is combinedwith line-finder saving circuits for further saving of diallingswitches.

Fig. 1 shows a conventional circuit for connecting a subscriber AB to asubscriber A31 by way of an exchange of which the subscriber AB isconnected to a free register RG by way of a first line finder 0Z1, asecond line finder 0Z2, a connecting circuit VC and a register finderR2. The numerical connecting path in accordance with the digits dialledby subscriber AB is set up under the control of the register RG by twostages of group selectors 6K1, and GKz and one stage of final selectorsEK in cascade. The first group-selector (3K1, is adjusted in accordancewith the first figure, the group selector 6K1 selecting a free secondgroup selector 6K2 from the group having access to the directiondesired. The adjustment of selector GK1 may start upon reception of thefirst digit by the register RG. Similarly, the second group selector GKzis subsequently adjusted in accordance with the second digit, whereafterthe final selector EK selects the desired line A31 in accordance withthe last two digits of the number dialled.

If 4,000 lines are connected to the exchange, the numbers of switches0Z1, 0Z2, GK1, 6K2 and EK of the various stages and the number ofconnecting circuits VC are required to be 400, 184, 184, 192, 400 and184, respectively, in order to deal with a mean incoming trafiic of 3Erl. per subscribers with a possibility of stagnation per selectingstage smaller than 0.002. Consequently, the total number of switchesrequired per 100 outlets is 1,360. Said numbers are under the sameconditions 900,. 414, 414, 594, 900 and 414, respectively, in anexchange for 9,000 subscribers, so that the total number of switches inthe various connecting paths is 3222.

Fig. 2 shows two groups of final selectors EK, each associated with agroup of 100 subscribers A81 and A32 respectively. In order to deal withan incoming tralfic of 3 Erl. per 100 subscribers with a possibility ofstagnation of 0.002 at the most, each group, similanly as in the circuitof Fig. l, is required to comprise 10 final selectors. However, for thesake of simplicity, only three final selectors of each group are shown,viz., the final selectors EKu, EKiz, EKis and EK21, EK22, EKzs re- 3spectively. The inlets of the selectors are connected to outlets U11,U12, U13, U21,'U22, U23 of second group selectors GK2, of which theinlets are connected to outlets V1, V2, V3 of first group selectors GK1,the arrangement being similar to that of the circuit of Fig. 1. However,the inlets ot the final selectors are furthermore connected directly tooutlets V11, V12, V21, V22, V31, V32, etc. of the first group selectorsGK1 in such manner that one outlet of each first group selector directlyhas access to one final selector of each group of final selectors EK.For this purpose the first group selectors GK1 are divided into a numberof groups equal to the number of final selectors associated with eachhundred subscribers, groups in the case under consideration. Figure 2shows three such groups of first group selectors GK1, each group for thesake of simplicity being shown as a single selector GKii, GKIZ and GK13,respectively. A first final selector EK11, EK21, etc. of each group isconnected directly to an outlet of the group of first group selectorsGKn, a second final selector EK12, EKzz of each group is connected to anoutlet of a second group of first group selectors GK12, a third finalselector EK13, EK23 of each group is connected to an outlet of a thirdgroup of first group selectors GKia, etc.

A calling subscriber is connected by way of a line finder OZzi, OZ22,0223 and, if necessary, line finders of one or more further stages to aconnecting circuit VC1, VCQ or VC3, associated with one of the firstgroup selectors GKi, for example GKn, whilst furthermore a register R6is connected by way of a register finder RZ to the said connectingcircuit. The number of telephone connections, as before, is more than1,000. The register stores the first digit until the second digit isreceived. At this moment it is determined to which group of 100 (groupAB1 or AB2, etc.) the called subscriber belongs, so that it is alsoknown via which group of final selectors the connection is required tobe set up. Assume that the called subscriber is in group A131 connectedto out lets of the final selectors EKu, EK12, EKis, etc. The registerfirst determines whether the final selector EKu of the desired group,connected directly to an outlet of GKu, is free, in which event GK11 isset to the outlet concerned, whereupon the final selector EKn is set inknown manner to the called line. The setting of the first group selectorGK11 takes place in accordance with two figures, i. e. in a manner whichis similar to that of a final selector.

In the case assumed, only one final selector of each group is connecteddirectly to an outlet of a determined group of first group selectors.However, if a suificient number of outlets of the first group selectorsis available,

it is possible to cause the first group selector to give access directlyto two or more final selectors of a group, that is to say without theintermediary of a second group selector GKZ. In such a case, the firstgroup selector GK1 makes a free choice from the directly connected finalselectors EK of the desired group.

If no such direct connection to a final selector EK is free, the firstgroup selector GKn is set by the register in accordance with the firstdigit to a free second group selector (3K2, whereupon the latter is setnormally in accordance with the second digit to a free final selector EKof the desired group.

For the first final selectors EKii, EKzi, etc. of each group there is apreference to be engaged by way of one of the first group selectors GKn,for the second final selectors EK12, EKaz, etc. of each group there is apreference to be engaged by way of one of the first group electors EK12,etc. However, since for each final selector EK of a group there is apreference to be engaged by way of a definite difierent group of firstgroup selectors 6K1, the number of connections to be dealt with is, onthe average, equal for the various final selectors EK of a group, thatis the probability of being free is the same for all final selectors EKof the group.

With an incoming traffic of 3 Erl. per 100 subscribers, on the averagethree final selectors EK are operative and hence 7 final selectors EK ofthe group of 10 are free. When a direct outlet to a final selector EK istested by a first group selector 6K1, the probability of the said finalselector being free is thus 70%. Consequently, on average 70% of thetrafiic is routed through direct connections between first groupselectors GKr and final selectors EK. This trafiic takes place withoutthe intermediary of the second group selectors 6K2. The latter thus haveto deal with only a comparatively small proportion of the total incomingtrafiic, viz. 30%, so that the number of second group selectors GKz maybe much smaller than in a system as shown in Fig. 1. In determining thenumber of second group selectors (3K2 it is also germane that thepossibility of stagnation of this stage may be assumed to be somewhathigher than normal, that is to say 0.002, since part of the tratfic isrouted through direct connections. The possibility of stagnation may nowbe 0.0066, which results in a further reduction in the number of secondgroup selectors GKz required.

In an exchange for 4,000 subscribers, the subscribers are divided into40 groups of 100 each. 40 of the 100 outlets of the first groupselectors GKi are reserved for direct connections with final selectorsEK, the other outlets, divided into four groups of 10 outlets, beingaccessible to four groups of second group selectors 6K2 and a group of20 outlets being available for outgoing trafiic. The total numbers offirst group selectors GK1 and final selectors in the exchange are inthis case 184 and 400 respectively with an incoming tratfic of 3 Erl.per 100 subscribers and a maximum possibility of stagnation of 0.002.The number of second group selectors is however 68, which is an economyof 124 selectors, relative to a system as shown in Fig. 1.

In an exchange for 9,000 subscribers, the subscribers are divided intogroups of 100. In this case, the number of outlets available on switcheshaving outlets is not sufiicient to give each first group selector GK1directly access to a final selector EK of each group and also to secondgroup selectors (3K2. In this case, the first group selectors GKimayadvantageously be made in the form of switches having two hundredoutlets, divided into two sets of 100 each, which groups cooperate withdifierent sets of wipers. The 90 final selectors EK connected directlyto a determined group of first group selectors GK1, are then connectedto the first set of 100 outlets, the second group selectors beingconnected to the second set of outlets, divided into 9 groups of 10, inaccordance with the nine different directions of main trafiic. Theregister RG first determines via wipers of the first set, whether thedirectly connected final selector BK of the desired group is free,switchingover the first group selector GKI to another set of wipers ifthe said final selector EK is busy.

The numbers of first group selectors GK1 and final selectors EK requiredare, as before, equal to those required in a system as shown in Fig. 1,the number of second group selectors GKz being 153. Consequently, thenumber of dialling switches is in total 441 smaller. However, it is tobe noted that in the system shown in Fig. 1, use may be made of firstgroup selectors having 100 outlets, whereas in the circuit shown in Fig.2 the first group selectors in comparatively large exchanges require 200outlets, which switches are more expensive than those having 100outlets. If switches having 200 outlets are 40% more expensive thanthose having 100 outlets, the 414 first group selectors (3K1 having 200outlets are equivalent to 580 switches having 100 outlets, so that theeffective gain in switches is only 275 and not 441.

Although the connection of a first group selector GKi directly to afinal selector EK may fundamentally be effected by any known method,since it is substantially similar to that of a final selector, it isdesirable that the selectors should be set with the use of marking andmore particularly of selective marking. In this case, the outlets may bedistributed numerically in any arbitrary manner over the contact bank,whilst it is furthermore possible for the selectors to be adjustedinaccordance with two digits by a single movement and hence rapidly.

An example of a circuit for such control is shown diagrammatically inFig. 3. The circuit comprises a register RG, which may be connected byway of a register finder RZ to a first group selector GKi and to asecond group selector GK2 and a final selector EK. The relays areindicated in the drawing by capital letters and the associated contactsby corresponding small letters. The selectors GK1, GKz and EK eachcomprise a busy relay HG, HK, HE, respectively, each having two windingsHGi, HG2, HK1, HKz, H131 and HEz. The relays P and N in the register RGeach has two windings P1, P2 and N1, N2. The first group selector GK1comprises 200 outlets and comprises two sets of outlet contacts a1 b101, d1, e1 and as, hr, cs, d2, as, which cooperate with two differentsets of wipers. It is possible to change-over from one set of wipers tothe other with the use of changeover contacts. 0g1, Ogs, oga, 084, ogsof a switching relay 0G.

The dialing switches are adjusted by means of directvoltage comparison.The register RG comprises four marking switches MD, MH', MT, ME, whichare adjusted in known manner which will not be described further here,in accordance with the thousands, hundreds-, tensand units-digits of thenumber of a. called subscriber. The outlet contacts of the markingswitches are connected to voltage sources DV, HV,, TV, EV in such mannerthat the various contacts of each switch have different voltages appliedto them. The values of the said voltages are representative of thediiferent figures. Outlet marking contacts. of the dialling switches aremarked by direct voltages, the values of which are characteristic of thefigure of the group with which the outlet is associated. A voltagesource VD1, which is connected by way of contacts s1 and has to markingcontacts 01 of selector GK1, characterises the thousands digit of theoutlet of selector GKi upon test of the final selectors EK connecteddirectly to outlets of selector GK1. A voltage source VH, which isconnected by way of contact hes to marking contact d1 of selector GK1and to marking contact d3 of selector 6K2, characterises the hundredsdigit of the outlets of selectors GKi and GKz. Voltage source VDz, whichis connected by way of contact hkt to markingcontact d2 of selector GK1,characterises the thousands digit of the outlet of selector GKiuponhunting for a free group selector GK-z by selector VGKL Voltagesources VT and VE characterise the tensand the units-digits respectivelyof the lines connected tooutlets of selector EK.

The register RG comprises two voltage comparison devices NW1 and NW2(shown diagrammatically), which may be of known construction and whichhereinafter will briefly be referred to as zero switches," for comparingthe comparative voltage selected by a marking switch with the numericalmarking voltage of an outlet contact of a switch to be adjusted, whichmarking voltage is tested by the register RG via a wiper of the switch.

It the compared voltages at the inlet points 11, I2 and Is, 14respectively of the zero switches are different, the outlet points U1and U2 of the zero switches have comparatively high voltages, so thatthe rectifiers G1 and G2 are conductive andthe voltage of point U isalso comparatively high. A tube B is then conductive and test relay Tincluded in its anode circuit is energized. If the voltages compared bya zero switch are equal, which im plies that an outlet of the switchcorresponding to the desired digit is reached, the zero switch decreasesthe voltage of its outlet point U1, U2 respectively, so that theassociated rectifier is cut oft. If contacts 02 and ma are open, zeroswitch NW is inoperative. If," now, zero switch NW2 finds equality ofvoltage, the voltage of point Us and hence the voltage: of point Udecrease to such extent that tube B is cut off and relay Tisde-energized. In the event of contact 02' and/or contact m3 beingclosed, the two zero switches must simultaneously find voltage equalityto cause a decrease of the voltage of point U such that relay '1 may bede-energized, since if only one zero switch, for example NW1, were torespond, the voltage of the outlet point U2 of the other zero switchremains comparatively high, so that the voltage of point U also remainshigh and tube B is not cut off.

When the units digit is received, contacts mm, mm, mes, mel, mes areclosed and contact mes opens, the contacts me being associated with themarking switch ME. The relay T normally is energized. Due to contact me;being closed, rotary magnet DG of the first group selector 6K1 includedin a circuit extending from earth via contacts H184 and t2, winding ofrelay Hf, wiper; and marking contact e of register finder RZ, contacthgs and the rotary magnet DG to the negative terminal of a batter BA(not shown), the positive terminal of which is connected to earth, isenergized so that the group selector 6K1 is actuated for finding adirectly connected final selector EK of the desired group. At the sametime relay H in the said circuit is energized. The thousands-digitmarking voltage VDl is now compared by the zero switch NW1 via contacts.91 and hes, marking contacts 01 and wiper of selector G'Kl, contactoga, contact hgz, contacts and wiper b of finder RZ, and contact menwith the comparative voltage DV, which is supplied by way of markingswitch MD, contacts oa'and m1 to the inlet I1 of zero switch NW1. At thesame time, the zero switch NW2 tests by way of inlet point 14, contactmes, wiper and contact c of register finder R2. and contacts hgs and01:4, the hundreds-digit marking voltage VH of the outlets of groupselector GK1, which is supplied by way of contact hes to marking contactd1 of selector GK1, by comparing the said voltage with the voltage HV,supplied by Way of marking switch MH and contacts 04 andmz to the inletpoint Is of zero switch NW2. During the hunting movement, the outletsare thus only tested via contacts of the first set of wipers c1 and d1.As mentioned before, the numerical marking voltage is removed frommarking contacts of busy outlets, for example, due to the said contactsbeing connected to earth. If the directly selected final selector BK ofthe desired group is free, the zero switches NW1 and NW2 upon reachingthis outlet respond simultaneously, so that test relay T isde-energized. Due to contact t2 being opened, the circuit for energizingrotary magnet DG is interrupted, the selector GK1 stopping on the outletof the final selector EK. Contact is opens the circuit for energizingrelay H, so that this relay is de-energized a short time after relay T.Relay HG is energized by way of contact mm and the contacts t1 and I'll,wiper and outlet contact a of switch RZ, contact 11,91 and winding HGi.Relay HG is held energized by way of its second winding H62 and contacthgt, connecting the wiper d1 of selector GK1 through contact hgs andcontact 034 to earth, so that the hundredsdigit marking voltage VH-isremoved from the marking contact d1 and the outlet is marked busy. RelayHG connects several control lines through to wipers of the switch 6K byway of its change-over contacts km. 1232, hgs and hgs. When contacts hgzand hgs are opened, the

numerical marking voltages of the inlet points 12 and I4.

of the zero switches NW1 and NW2 are removed, so that relay T againenergizes, followed after a short time by relay H. Contact t1 opens thecircuit for energizing relay HG by way of its first winding HGl, beforethe con tact hgr closes, so that the relay HE of the final selectorcannot yet energize. Subsequently, relay M is energized by way ofcontacts ts, ha and or. Relay M connects the inlet points 11 and 13 ofthe zero switches by way of its contacts m1 and mz'to the tens-digitmarking switch MT and the units switch Rotary magnet DE of GKl, contactOgs, contact hgs, contact, and wiper e of finder RZ, winding of relay Hand contacts is and met to earth. In this circuit relay H in theregister RG and relay S in the final selector EK are energized. Theconnection of point U by way of contacts I12 and ts to earth preventsthe relay T from being de-energized, either during or afterswitching-over'the inlet points I1 and Is of the zero switches tosubsequent marking switches, before contact h2 opens upon energisationof relay H.

During the movement of the final selector EK, the zero switch NW1 teststhe tens-digit marking voltage VT of the outlet of EK by comparing itwith the comparative voltage TV adjusted by marking switch MT. Thetensdigit marking voltage at marking contact (:4 of the final selectorEK is supplied by way of contacts s2 and Jzez, marking contact and wiperIn of selector GKi, contacts ogz and hgz, contact and wiper b of finderRZ and contact me2, to inlet point I2 of zero switch NW1. At the sametime, zero switch NW2 compares the units-digit marking voltage EVselected by marking switch ME with the units-digit marking voltage VE ofthe outlet marking contacts d4 of final selector BK. The voltage VB issupplied by way of wiper d4, contacts s1 and hes, marking contact andwiper c1 of selector GKI, contacts age and hgs, wiper and contact c offinder RZ and contact mes to the inlet point 14 ofzero switch NW2. Assoon as the desired subscribers line has been found, the ,two zeroswitches NW1 and NW2 respond and relay T is deenergized. Due to contactt2 being opened, rotary magnet DE is tie-energized and the selector EKstops and after a short delay relay H is de-energized. Relay HE is thusenergized by way of contacts mm, 21 and hi, wiper and contact a offinder RZ, contacts hgi and ogi, wiper and marking contact an ofselector GKi, contact 11:21, and winding HEI. Relay HE closes a holdingcircuit for itself through its second winding HE2, contact hes, markingcontact and wiper d1 of selector GKi and contacts ogi and lzgs. Theadjustment of the selection path is thus completed.

If the final selector EK of the desired numerical group, which isconnected directly to selector GKi is busy, the zero switches NW1 andNW2 do not respond and the selector GKi continues to rotate. Theregister RG comprises a time-relay F, which is normally energized viacontacts I14 and f2. Due to the response of relay H, the said energizingcircuit is interrupted, but the relay F cannot be de-energizedimmediately since the said circuit is shunted by capacitor C, so thatcurrent flows for some further time through the winding of relay F. Ifswitch GKi were to have found a free final selector BK within a certaintime, the initial circuit for energizing relay F would again have beenclosed by way of contact hi upon de-energisation of relay H. The time ofdeenergisation of relay F is chosen to be such that switch GK1 can passall outlets at least once during this time. If the directly connectedfinal selector EK is busy, selector GKi does not find a free outletwithin the said time and the time-relay F is deenergized. Due to thedc-energisation of relay F, the winding P1 of relay P is energized byway of contacts mes, 0s and f1. Relay P is energized and closes, by wayof contact p2, a circuit for energizing relay 0, which is held energizedvia contact 05. Due to the energisation of relay 0, the energizingcircuit of winding P1 is opened at contact as, but relay P remainsenergized for some further time in a circuit extending via contact 01,winding P2 of relay P, wiper and contact d of finder RZ, and the windingof a switch-over relay 0G, which relay is energized in the said circuit.Relay 0G closes a holding circuit for itself by way of contact Ogs,short-circuiting at the same time the winding P2 of relay P by way ofcontact age, so that relay P is deenergized. So long as relay P isenergized, point U is connected to earth by way of contact p whichprevents relay T from being deenergized. Relay 0G connects the groupselector GKi by way of change-over contacts ogi, ogz, Ogs, 0g4 and ageto the other set of wipers. Due to contact 02 being opened, the zeroswitch NW1 is made inoperative. Contact 03 connects, by way of contacts111 and 2212, the wiper of the thousands-digit marking switch MD to theinlet point Is of zero switch NW: and contact 04 interrupts theconnection between inlet point Is and the marking switch MH.

The group selectors GKi and GK2 are adjusted in conformity with a singledigit under the control of zero switch NW2 only. After it has been foundthat a final selector EK is not directly available, the group selector(3K1 hunts for a free second group selector GK2 in accordance with theselected thousands digit. Zeroswitch NW2 for this purpose tests thethousands digit marking voltage VDz of the outlet marking contacts d2 byway of contacts age and hgs, contact and wiper c of finder RZ andcontact mes, by comparing it with the thousands-digit marking voltage DVselected by switch MD. As soon as a free group selector 6K2 has beenfound, relays T and H are successively tie-energized so that relay HG isenergized by way of contacts mer, hi and 11 in the manner previouslydescribed. After relay T has again been energized, the winding N1 ofrelay N is energized by way of contacts it, its and 07. Relay N is heldenergized by way of winding N2 and contact as. Contact n1 connects thehundreds marking switch MI'I by way of contact me to inlet point Is andthe connection of inlet point Is interrupts with switch MD.

Subsequently, after relay T has been energized, relay H is energized, inseries with rotary magnet DK, via contact hks, marking contact and wipere2 of selector GKi, contacts age and hgs, contact and wiper e of finderRZ, winding of relay H and contacts t2 and "184. During the movement ofselector GKz, Zero switch NW2 tests the hundred-digit marking voltage VHof the outlet marking contacts (13 of selector GK2 by way of contacthka, marking contact and wiper c2 of selector GKi, contacts Ogs and hgs,contact and wiper c of finder RZ, and contact mes. As soon as a finalselector EK of the desired group has been found, the zero switch NW2responds and the relays T and H are successively de-energized. Due tothe de-energisation of relay T, relay Q is energized in a circuitextending via contacts t4 and ns. Relay Q is held energized by way ofcontact (11. Contact 12 interrupts the circuit of rotary magnet DK, sothat selector 6K2 stops. Relay HK is energized by way of winding HKi,contact hki, contact and wiper (12 of selector 6K1, contacts ogi andhgi, contact and wiper a of finder RZ and contacts hr, t1 and mm. RelayHK through-connects several control wires to Wipers of the selector GK2by way of changeover contacts hki, hk2 hks and hks, closing by way ofcon tact 11/01 a holding circuit for itself extending by way of contactshgs and 0g4, wiper and marking contact (12 of selector GKI, contact hkiand winding HK2. Due to the closure of contact like, the marking voltageis removed from the marking contact (is of selector 6K2, the outletbeing marked busy. Zero-switch NW2 reacts upon the opening of contacthks, increasing the voltage of its outlet point U2, as a result of whichrelay T again responds and contact t1 opens the circuit for energizingrelay I-IK via its firstwinding. After relay T has been energized relayM is energized by way of contacts 14, I13 and 07 Relay M is heldenergized by way of contact m4, connecting by way of its contacts m1 andma, the marking switches MT and ME to the inlet points I1 and is of zeroswitches NW1 and NW2. Due to the response of relay T, the relay H in theregister RG and the relay S in the final selector EK are energized inseries with rotary magnet DE. Subse quently, the final selector EK isadjusted to the desired numerical outlet, zero switch NW1, of which theoutlet point U1 is now connected'by way of rectifier G1 and con- 9 tactms to the point U, testing the tens-digit marking voltage by way ofcontact mez, wiper and contact b of finder RZ, contacts hgz and ogz,wiper and marking contact b: of selector 6K1, contact hkz, wiper andmarking contact b of selector GKz and contacts hezand s2 to wiper c4 ofselector EK. Zero switch NW2 at the same time tests the units-digitmarking voltage VE of the marking contacts d4 of selector EK by way ofwiper and marking contact of finder RZ, contacts hgs and Oga, wiper andmarking contact as of selector 6K1, contact hks, wiper and markingcontact ca of selector 6K2, contacts hes and s1, and wiper d4 ofselector EK. When the desired outlet is reached, the two zero switchesNW1 and NW2 response simultaneously, so that the circuit for energizingthe rotary magnet DE is interrupted and selector EK stops. Relay HE isenergized by way of contacts mer, t1 and hi, wiper and contact a offinder RZ, contacts hgr and ogr, wiper and contact 02 of selector GKr,contact hkr, wiper and contact as of selector GKz, contact her andwinding HEi. Relay HE closes a holding circuit for itself by way ofcontact hks, wiper and marking contact d3 of selector GKz, contact hesand winding HEz. The adjustment of the selection path by way of thegroup selectors GKr and GK-z and the final selector EK is thuscompleted.

Fig. 4 shows a writing diagram for a system for more than 10,000subscribers, for example for 50,000 subscribers. The subscribers areconnected in groups of 10,000 to 5 difierent exchanges and arecharacterized by a number consisting of five digits. The first digitdetermines the exchange with which a subscriber is associated, the fourother digits indicating the thousands, hundreds, tens and units digitsof the subscribers number within the exchange. Figure 4 shows a cascadeof four numerical selecting stages, a first group selector stage 6K1, asecond group selector stage GKz, a third group selector stage 6K3 and afinal selector stage EK. Said selecting stages are provided in one ofthe exchanges. The other exchanges are similarly arranged.

Second group selectors GKZI are connected to the outlets an of the firstgroup selectors 6K1. The outlets m2 of selectors 6K1 give access to theother exchanges. The group selectors GK1 which for this purpose aredivided into groups in a manner similar to that described with referenceto Fig. 2, each give direct access, via outlets are, to one finalselector of each group of final selectors EK. The traific from otherexchanges is led via second group selectors GKzz. The outlets uzr of thesecond group selectors GKzr and GKzz are connected to third groupselectors GKa. The second group selectors GKzl and GK22 also have directaccess to a final selector EK of each group via outlets u22. The secondgroup selectors GKz, similarly as the second group selectors GKi, aredivided into a number of groups equal to the number of final selectorsEK per group. The second group selectors GKzr, which are connected tooutlets of first group selectors 6K1, give direct access to finalselectors EK other than those to which the first group selectors GKrhave direct access.

A calling subscriber is connected to a register RG by way of one or morestages of line finders OZ, a connecting circuit VC and a register finderRZ. After the first digit has been received, it is determined to whichexchange the called subscriber belongs. If it is found that a subscriberof another exchange is concerned, the register RG- adjusts the groupselector GKI, in conformity with this digit, to a line L1 leading to theexchange concerned. However, the register does not adjust of the firstgroup selector (3K1 until the third digit is received, if the connectionis tobe established within the same exchange. At this moment it isdetermined through which group of final selectors EK the connection isto be set up. The register RG then first tests, in conformity with thesecond and the third digit, the final selector of the group concernedwhich is connected directly to selector GKi. If

this final selector EK is free, the register RG adjusts the selector GKrto it and subsequently the-final selector EK in conformity with the lasttwo digits. However, if the direct outlet is busy, the first groupselector is adjusted to any free second group selector GKzi, whereafterthe register RG again investigates with reference to the second andthird digits Whether the outlet 1122, which gives direct access to afinalselector EK oi the desired group, is free or busy. This is a finalselector EK of the group other than that which has been tested via thefirst group selector GKi. If the directlyconnected final selector isfree, the second group selector GKzi is adjusted thereto and theconnection with the called subscriber is set up by way of the said finalselector EK. If this final selector EK is busy, the register RG adjuststhe second group selector GKzi in conformity with the second digit,subsequently the third group selector in accordance with the third digitand finally the final selector 'EK.

Upon a call coming through a line L2 from another exchange, the secondgroup selector GKzz is adjusted in a manner similar to that describedabove for the second group selector GKzi.

Since at first for each stage a direct connection to a final selector istested, a considerable part of the traffic takes place without theintermediary of the second and/ or third group selectors, so that thelatter have to deal with a comparatively low trafiic density and thusmay b comparatively small in number.

The numbers of switches GKr, GKZI, GKzz, GK: and EK per exchange are610, 146, 224, 150 and 1,200, respectively, if it is assumed that atrafiic of 4.2 Erl. per lines comes in and that A of the trafiic is ledvia outlets m2 of selector 6K1 to other exchanges and /3 of the trafficflows back to the exchange by way of group selectors GKzz and that themaximum possibility of stagnation per selecting stage is 0.002.Consequently, the total number of selectors per exchange is 2,330. Sincethe selectors GKi, GKzi and GKzz have each 200 outlets, the equivalentvalue of all dialling switches of the exchanges together is 2,702expressed in value relative to switches having 100 outlets. If no directconnections between the outlets of selectors (3K1 and of GKz and finalselectors EK were used, the numbers of selectors GKr, GK21, GK22, GKsand EK would be 610, 448, 224, 924 and 1,200 respectively and hence intotal 3,406, in which event all switches require only 100 outlets.

Further modifications are possible in that the first group selectors,for example, may give direct access to third group selectors, whilstanalogous principles may be used with systems having more than 100,000subscribers, in which event the number of exchanges, each for 10,000subscribers, is larger than 10. In the latter case, the subscriber linesare characterized by six figures, of which the first two figuresindicate the exchange, it being possible for connections to be ledthrough a cascade of five stages of selection, whereby one or morestages of selection in the numerical connection path may be passed bydirect connections between stages of selection normally separated byintermediate stages. The circuits described permit of economy inselectors of intermediate stages of selection. Further economy inswitches may be obtained by the use of line-finder saving circuits. Anexample of such a circuit for an exchange of 9,000 subscribers is shownin Fig. 5 in which two main groups of connecting circuits VGA and VCBare used, which may be connected by way of a register finder R2 to aregister RG. The inlets of the connecting circuits VCA are accessible byway of a single stage of line-finders OZA to the subscriber lines AB. 7The inlets of the con necting circuits VCB may be connected by way oftwo stages of line finders 028 and (DZ-BK or by way of three stages ofline finders OZB, OZ-GK and OZ--EK to a calling line. The outlets of theconnecting circuits VCA may be connected by way of two stages GKA andOZEK or by way of three stages GKA, OZ-G'K and OZ-EK of numericalselectors to a calling line. Similarly, such a connection between theoutlets of the connecting circuits VCB and a called line may extend viatwo stages GKB and OZEK or via three stages GKB, OZ-GK and OZ--EK ofnumerical selectors. Consequently, the switches OZ-GK and OZEK may beused either for connecting a calling line to a connecting circuit or forconnecting a connecting circuit to 9. called line, in other words, thesaid switches may fulfil the function of either line finder or numericalselector. The adjustment of the line finders otherwise takes place in anexactly similar manner as that of selectors and this in both casesnumerically in conformity with the number of a subscriber.

Nine groups of line finder-group selector switches OZGK are multipled todetermined outlets of the switches GKA, GKB and OZB. The inlets of theline finder-final selector OZ-EK are multiplcd to outlets of theswitches OZGK. and are also each multipled to outlets of the switchesGKA, OZB and GKB, so that each switch gives direct access to one linefinder-final selector of each group. The number of line finder-finalselectors OZEK per group is with an assumed trafiic of 3 Erl. per 100lines and a chance of stagnation of 0.002. The switches GKA, GKB andOZB, similarly as in the circuit shown in Fig. 2, are divided into anumber of groups equal to the number of line finder-final selectorswitches OZEK per group and hence, in this case, 10 groups.

Each group of 100 subscribers has associated with it a common calldetector OD. Upon a call in the subscriber group concerned, the calldetector OD responds, hunts and identifies the last two digits of thenumber of the calling subscriber for the subscribers line by means of anidentification finder IZ. Since each call detector OD is associated witha definite subscriber group, the thousands and hundreds digits of thesubscribers number are also identified. The call detector OD engages afree register RG by way of an auxiliary selector KH, transmittingthereto the subscribers number.

Each group of subscribers has associated with it four connectingcircuits VCA, which may reach the subscribers concerned by way of asingle line finder OZA. The exchange thus comprises a total of 360connecting circuits VCA with the associated line finders OZA and firstgroup selectors GKA.

The register RG receives from the call detector OD a signal signifyingwhether a connecting circuit VCA associated with the group of thecalling subscribers is free or busy and if free, engages it, whereafterthe line finder OZA is adjusted to the calling line. If no connectingcircuit VCA is free, the register RG engages any free connecting circuitVCB by way of the register finder RZ. Since there is a comparativelygreat possibility that a free connecting circuit VCA is available (80%with an incoming tratfic of 3 Erl.) a considerable propor- OZB isadjusted thereto, whereafter the finder selector .OZ-EK is adjusted tothe calling line.

If the direct connection to the switch OZEK is busy, connection isestablished by way of the switches OZB, OZGK and OZEK in cascade. Theswitches are controlled wholly numerically, that is to say, as diallingswitches, with reference to the digits of the subscribers number that isto say, the switches OZB and OZ-GK in the manner of a group selector inconformity with the first and second digits, respectively, a freeselection taking place from the group of outlets leading in the desireddirection of traffic, whilst the line finder-final selector OZEK isadjusted in conformity with the last two digits in the manner of a finalselector.

A connection between a connecting circuit VGA or VCB and a calledsubscriber is established with reference to the dialing signals receivedby the register RG in an. exactly similar manner as the connection witha calling line. A considerable proportion of the connections isestablished without the intermediary of the switches OZ- GK and takesplace via direct connections between the outlet of switches GKA, GKB orOZB and the line finderfinal selectors OZEK. The total number ofswitches OZGK is 210.

Since the line finder connecting path between a connecting circuit and acalling line may be constituted by one switch (OZA), by two switches(OZB and OZEK), or by three switches (OZB, OZGK and OZEK) and thenumerical selection path between a connecting circuit and a calling linemay be constituted by two switches (GKA or GKB and OZEK) or by threeswitches (GKA or GKB, OZEK and OZGK), the speech connection between acalling subscribed and a called subscriber may comprise 3, 4, 5 or 6switches. In the majority of cases, the line-finder path comprises onlyone switch and the selection path comprises only two switches so thatthe connection between the calling subscriber and the called subscribertakes place through only three switches. The probability of theconnection comprising six switches is small. The fact that, undercertain conditions, three stages of line finders in cascade may be used,implies that in principle, the connecting circuits VCB are accessiblefor all calling lines, so that the number of con necting circuits VCBmay be smaller than if at the most two stages of line finders areavailable and hence not all of the connecting circuits VCB areaccessible to all subscribers.

The total number of switches through which speech connections may takeplace is 1,966, whereas 3,222 switches would be required with a systemsimilar to that shown in Fig. 1 under the similar conditions.Consequently, the number of switches is 1,256 smaller. However, it is tobe noted that the switches GKA, GKB and OZB require 200 outlets each.Consequently, the value of the speech-path switches in the exchange isabout equivalent to that of 2,165 switches having outlets each, so thatthe effective gain is 1,057 switches. Expressed in switches of 100outlets, the value of the speech-path switches with a system similar tothat shown in Fig. 1, is 50% higher than with that of Fig. 5. Apart fromthe fact that the value of the switches is considerably smaller, it isto be considered that in a circuit as shown in Fig. 1 3,222 switches andin the circuit shown in Fig. 5 only 1,966 switches are in need of spaceand maintenance, so that there is also gain in the maintenance and spacecosts.

What I claim is:

1. A circuit for use in automatic signalling systems comprising at leasttwo stages of group selectors in cascade,

each of said selectors having an inlet and a plurality of outlets, thefirst of said stages comprising a plurality of selectors and the last ofsaid stages comprising at least one selector, a register for controllingthe numerical setting of said selector stages, the outlets of theselectors of the last of said group selecting stages being divided intoa plurality of numerical groups, means for coupling the inlet of saidselector of the last group selecting stage to an outlet of each of theselectors of the first group selecting stage, the groups of outlets ofthe last selector stage being numerically distinguished by at least twodigits and the 1 groups of the selectors of the last stage beingnumerically distinguished by the penultimate digit of the groups ofoutlets thereof, means interposed between the outlets of said selectorof the last group selecting stage and the remaining outlets of selectorsof the first selecting stage to provide direct connections,respectively, between said remaining outlets of each group selector ofthe first selecting stage and an outlet of each numerical group ofoutlets of the last group selecting stage, said register being adaptedto provide a numerical connection between the inlet of a selector ofsaid first group selecting stage and a numerically desired outlet of thelast group selecting stage comprising means for setting the selector ofthe first group selecting stage to a free outlet connected directly toan outlet of the numerically desired group of the last group selectingstage, the selector of said first stage being controlled incorrespondence with said at least two digits of the desired group ofoutlets, and means for setting the selector of the first group selectingstage in correspondence with the penultimate digit of the desired groupof outlets to a free outlet thereof to which the inlet of a selector ofthe next following group selecting stage in the cascade is connected inthe event no free outlet of said first stage connected directly to anoutlet of the numericallly desired group of the last group selectingstage is available.

2. A circuit as set forth in claim 1 wherein the selectors of the firstgroup selecting stage are divided into a number of groups equal to thenumber of outlets per numerical group of outlets of the selectors of thelast group selecting stage, the outlets of each numerical group of saidoutlets of the last group selecting stage being connected directly tooutlets of different group selectors of the first group selecting stage.

3. A circuit as set forth in claim 2 further including a plurality ofconnecting circuits, a line finder second group selector, a linefinder-final selector, a calling line and a called line and wherein theselectors of the first group selecting stage are divided correspondingto the outlets thereof into two main groups, each inlet of the selectorsof one main group being connected to the inlet of one of said pluralityof connecting circuits, each inlet of the selectors of the other maingroup being connected to the outlet of one of said connecting circuits,the outlets of the selectors of the one main group being multipled tocorresponding outlets of selectors of the other main group and connectedin one condition to an inlet of said line finder second group selectorand in another condition to an inlet of a line finder-final selector ofwhich the inlet is connected to an outlet of said line finder secondgroup selector, an outlet of said line finder-final selector beingconnected to said called line, means for connecting one of saidconnecting circuits to said calling line in one condition via a selectorof the one main group of the first group selecting stage and a linefinder-final selector and in another condition via a selector of onemain group of the first selecting stage, a line finder second groupselector and a line finder-final selector, and means for connectinganother one of said connecting circuits to said called line in onecondition via a selector of the other main group of the first groupselecting stage and a line finder-final selector and in anothercondition via a selector of the other main group, said line findersecond group selector and a line finder-final selector.

4. A circuit as set forth in claim 3 further including a direct linefinder, an inlet of one of said connecting circuits being connected tothe inlet of said direct line finder, and the outlets of said directline finder being connected to subscriber lines, whereby saidlast-mentioned connecting circuit may be connected to said calling linevia said direct line finder.

References Cited in the file of this patent UNITED STATES PATENTS2,305,779 Hebel Dec. 22, 1942 2,431,313 Den Hertog Nov. 25, 19472,431,692 Hersey Dec. 2, 1947 2,484,080 Deakin Oct. 11, 1949 2,529,166Lesigne Nov. 7, 1950 2,629,019 Lesigne Feb. 17, 1953 2,642,499 GohorelJune 16, 1953

